Inductive-coupling device



1,625,723 Aprll 1927' M. HULL ET INDUCTIVE COUPLING DEVICE 'Filed Dec. 27. 1922 2 Sheets-Sheet 1 April 19 1927.

L. M. HULL ET AL INDUCTIVE COUPLING DEVICE Filed Dec. 1922 2 Sheets-Sheet 2 Patented Apr. 19, 1927.

UNITED STATES PATENT OFFICE.

LEWIS M. HULL, OF MOUNTAIN LAKES, AND RICHARD W. SEABURY, OF BOON'I'ON, NEW JERSEY, -ASSIGNOBS TO RADIO FREQUENCY LABORATORIES, INCORPOIBATED, 01F BOONTON, NEW JERSEY, A CORPORATION OF"NEW JERSEY.

INDUCTIVE-GOUILING DEVICE.

Application filed December 27, 1922. Serial No. 609,230.

This invention relates to devices employed for the inductive coupling of electric circuits and more particularly to inductive coupling devices of the typecomprising a stator and rotor Itis an object of the invention to provide an inductive coupling device in which the maximum efiiciency is attained by reducing the clearance between the stator and rotor windings to a minimum. An objectof the invention is to provide an inductive coupling device having two windings and in which the leakage of magnetic flux between the windings is reduced to a minimum. A further object is to provide a completely shielded inductive device for use at radio frequencies in which device the winding or windings and the shield are so disposed that the shielding is attained without high eddycurrent losses. A further object is to provide' an inductive coupling device having windings thereon which constitute two separate electrical circuits and in which the leakage of magnetic flux between thewindings is maintained at a minimum regardless of the absolute magnitudes of the involved selfand mutual inductances, and more specifically an object is to provide a novel form of winding material particularly adapted for use in the construction of coupling devices of the type stated.

These and other objects of our invention will be apparent from the following description when considered in connection with the accompanying drawings which illustrate. various embodiments of our in vention, and in which- Fig. 1 is a po ective view of a variotransformer em ying our invention',

Fig. 2 is a perspective view of the rotor,

Fig. 3 is a perspective view of one of the stator elements,

Fi 4 is a sectional detail in perspective and illustrating the double winding in position on the rotor,

Fig. 5 is a perspective view of a shielded transformer, as viewed from the rear end,

Fig. 6 is a similar perspective view, partly in section, as taken from the front of the shielded vario-transformer, i

Fig. 7 is a vertical section through the rear closure of the shield,

Fig. 8 is a perspective view, partly in section, of a modified form of shielded variotransformer, and

Fig. 9 is a vertical section through a stator. and rotor, illustrating a modification in the construction of the stator elements.

In thedrawings the rotor is designated by the numeral 1 and comprises a portion of a right circular cylinder having parallel rece'sses 2, 2 extending around the outer face thereof for receiving windings. If desired, the rotor body may be slotted as at 3 to reduce the amount of material employed and to faci-liiate the winding operations, but this feature is not essential. The rotor l is provided with shafts 4, 4 which are prei ably hollow and serve as conduits for the terminals of the windings. The shaft 4' is of suflieient length to extend beyond the stator and serve as a support 'for an operating knob or dial 5 and is provided with a transverse opening 6 through which one set of terminals passes.

For convenience in manufacture and assembling, the stator preferably comprises two L-shapedmembers 7 having inner faces which conform to the shape of the outer surface of the rotor 1. The inner surface of each stator member comprises a thin web 8 .which is preferably a thin sheet of micarta or similar material, i. e., paper impregnated with a phenolic condensation product. To adequately support the thin web 8 and to define spaces for receiving windings, three parallel ribs 9 are arranged on the web members. The stator members 7 are conveniently formed by a molding operation in which the plastic composition, rubber, phenolic resin or the like, which is to form the ribs 9, is united to a pro-shaped web 8 which has been placed in a mold of the proper design. At the proper point, the central rib 9 of each stator member 7 is provided with an opening 10 which serves as a bearing for a shaft of the-rotor, and the two members 7 when assembled about the rotor may be held in position by suitable means, such as screws 11.

In variable inductive coupling devices, the closeness of the coupling between those portions of the windings carried respectively by rotor and stator, when the device is adjusted to give maximum or minimum coupling, is a material factor affecting the eflective range of inductance of the windings which may be secured. If the stationary and movable windings could be brought into contact at each end of the range of variation, optimum results would be attained, but it is obvious that this cannot be attained with a coupling device comprising a stator and a rotor. The construction as described above permits a very close approximation to such an arrangement however, since the web 8 which separates the stator winding from the rotor need not exceed 1/64 inch in thickness and may be thinner. The depth of the recesses 2, 2 of the rotor is so designed that the windings will lie just within the outer circumferential surface of rotor. Some small clearance may be allowed between the rotor and the web 8, but with careful construction such clearance is not necessary and the rotor may be supported by and journaled within the web 8 of the stator. lVhen no clearance is provided between the stator and rotor the adjacent faces of the stator and rotor windings will be spaced apart by a distance not materially greater than 1/6& of an inch and even this small clearance between the windings may be still further reduced by the use of a thinner sheet of material for the web 8. This provides an approach to physical coincidence of the stator and rotor portions of the two windings in their coplanar positions, which results in the close approximation to unity coupling which is necessary for an extended inductance range of. both primary and secondary windings.

When the maximum range in inductance of the windings is not essential, the clearance between the stator and rotor windings may be increased, as by providing clearance betweenthe rotor and stator or by the use of thicker sheets for the web 8. Alternatively, the thin web which separates the stator windings from the inner face of the stator member may be formed of the same material as the ribs. Such a construction is shown in Fig. 9, in which the web 8, as well as the ribs 9, is formed of hard rubber, phenolicoresin or the like.

The stator and rotor bodies may be used to support any desired type of winding, i. e. they may be wound to provide a variomete'r, a variocoupler or a vario-transformer. When wound as a vario-transformer the-stator and the rotor each carry a portion of the primary and of the secondary windings and the two portions of each winding are conneeted inseries.

When no clearance is provided between the rotor and stator it' is evident that the double windings must be carefully and com pactly arranged upon the rotor, as otherwise the outer layer might rub against the stator. By using a cable or double wire consisting of two insulated strands laid parallel to each other and encased without twisting or weaving in a thin layer of insulating material, the windings may be readily applied to the rotor. In Fig. 4, the two parallel strands of wire 12 are separated from each other by insulating material 13 which may be enamel or a wrapping of silk or cotton and the two wires are bound together by a silk or cotton wrapping 14. In addition to the mechanical advantages resulting from the use of a double wire of this construction, an electrical advantage is also obtained, since the capacity between the primary and secondary windings has no effect upon the currents traversing thewindings. This follows from the fact that substantially unity coupling between the the primary and secondary windings is obtained at all positions of the rotor; consequently, there is no difference in potential between adjacent points of the two windings, and no flow of current across the dielectric between adjacent turns. With these conditions the electrostatic capacity existing between the two windings has no effect upon the current flow.

To protect audions or other devices adjacent the coupling device from being influenced by the electric and magnetic fields set up by the passage of current thru the windings it is desirable to employ a shield around the same. Although it has been generally believed that concentrated inductance windings traversed by radio frequency currents could not be shielded by adjacent continuous metal shields, we have discovered that little or no loss in the efiiciency of a concentrated radio frequency inductance will result when the field is of proper form and the shield is properly spaced from the windings. Complete shielding without material loss in efliciency and without unduly increasing the overall dimensions of thedevice may be attained when the shield is so spaced from the windings that the magnetic field at points adjacent the inner surface of the shield is substantially parallel to said inner surface. In the form illustrated in Figs.

5-7, the shield comprises a section of square tubing 15 of metal such as iron, brass, or copper, surrounding the coupling device. The cap or closure 16 at one end of the tube 15 is provided with a central aperture 17 through which the shaft 4 of the rotor passes. The cap 16 bears an index mark 18 for cooperating with an appropriate scale on the dial 5, and also a stop lug 20 which projects within an arcuate slot 21 formed in the rear face of the dial. The cap 22 at the opposite end of the tube 15 carries binding posts 23 which are insulated from the cap 22 and which serve as terminals for the primary winding. The terminals of the secondary windings are similarly attached to another set of binding posts 24, 24' which are also carried by the cover 22. The low end of the secondary is grounded to the metfits snugly within the shield, but preferably spacing lugs 26 are provided for positioning the stator within the shield and these lugs may be integral with the stator members 7 or they may be attached to the stator members in any desiredhnanner.

In Fig. 8, we have shown a modified form of shiel and coupling device. The main body of the shield in this instance comprises a thin tube 27 of circular cross-section having closures 28 and 29 which correspond respectively to the closures 16 and 22 which are ample ed with the rectan larly shaped shield. e outer surface of t e stator members is shaped to the curvature of the inner surfaceof the tube. 27 and the size of the stator is such that it may fit snugly within the tube. To position the stator within the casing a strip 30 haying a width equal to that of a recess 2in'the stator may be soldered inside the tube 27. The stator may be spaced from the end closures b spacing lugs on the stator similar to the u above described or by projections on t e inner face ofthe closures, which rojections may also serve to 'tion the c osures with respect to the body of the shield. In this and with the uare shield,the closures may be secured to t e shield b soldering or brazing. It will-be noted that the windingsare elongated, having a length which is materially greater than'their width, and that the enc from the windings and its axis is substan- 'tially coincident with the axis of the windings. In actual use we have found that such a shield may be employed with windings traversed .b currents at a frequency as high tor and stator, a meta 26 as said windin means on said stator s acin the inner surosing shield is so positioned by the ribs of the stator that the shield is spaced.

We claim: 1.- An electro-magnetic coupling device of the type described, comprising two relatively movable elements, and primary and secondar windings formed by twin conductors on said elements, said relatively movable'elemerits comprising concentric surfaces of revolution, the outer element including a thin web carrying spaced ribs, forming grooves for receiving the windings. V

2. An elect-ro-magnetic coupling device as claimed in claim 1, in which the two relatively movable elements have the form of right circular cylinders of which thelength exceeds the diameter.

3. An inductive coupling device for use in radio frequency circuits comprising a web of non-conducting material, a winding thereon suitable for the conduction of radio frequency currents a metallic envelo enclosing said web and winding and shie ding thesame, and ribs of dielectric material on said web, spacing said envelop from said windcom risi a rotor having the form of a rtion o a right circular cylinder, whose ength is materially in excess ofits diam eter, a statorhaving an inner surface conforming to the she e of said rotor, primary and secondary win ings arran ed on said rolic envelo having the form of a right circular cylin er enclosing and shielding the same, and

face of said envelop t e outer layers of said windings and positioning said en velop with its axis substantially coincident with the axis of said rotor, stator and the "windings thereon.

5. In avariable coupling device-a stator assembly comprising two similar L-shaped members fitting together to form a stator element comprising a thin web conforming to a portion of. a surface of revolution ant ribs upon the exterior of said web arranged to form grooves I for the reception of the windings.

6. In avariable coupling device a rotor havin an outer face conforming to a portiono a surfaceof. revolution, and a stator comprising two L-shaped elements fitting togethe'r'to present interiorly a surface of rev olution concentricto that of said rotor.

4 A variable inductive coupling device 7 In a variable inductive cou' lin device comprisi two relatively mova 1e e ements and windings thereon, a metallic shield surroundin said elements and sfpaced from the outer e ement by means 0 ribs forming grooves for the reception of the windings.

In testimony whereof, we aflix our signatures. LEWISHM.

RICHARD W. SEABURY. 

